To seal rotating shafts of pumps, compressors and the like, it is known to provide a non-contacting shaft seal on the shaft, which includes an axially adjacent pair of seal rings wherein one seal ring rotates with the shaft and the other seal ring is non-rotatably connected to a seal housing. The seal rings each include an end face which faces axially wherein the seal faces are disposed in close opposing relation to define a sealing region extending radially between the outer and inner diameters of the seal rings. The fluid being sealed can either be a liquid or a gas, and the sealing region prevents or minimizes migration or leakage of the fluid radially across the seal faces.
More particularly, the seal faces typically are disposed in contact with each other when the shaft is not rotating to thereby define a static seal. Further, at least one of the seal faces includes a hydrodynamic face pattern that generates a fluid film between the seal faces during shaft rotation to reduce if not eliminate contact between the seal faces.
Hydrodynamic face patterns are known and include wavy faces, spiral grooves, T-grooves and the like. The face patterns are formed in the seal faces through various processes and typically involve providing a flat face and then removing material from the seal face to a very small depth.
For example, U.S. Pat. No. 5,529,317 (Muller) discloses several seal face patterns wherein one of the seal face patterns includes stepped hollows in the seal face that creates a hydrodynamic load support between the seal faces during shaft rotation. The rectangular stepped hollows are formed by means of laser beams which are applied in an overlapping manner.
While a rectangular shaped laser beam may be used to form the rectangular steps of the '317 patent, it has been found that when two adjacent passes of a laser beam overlap, the area of overlap between each adjacent pair of passes has an excessive depth since the overlap area is cut once on the first pass and then cut again on the second pass. In particular, during each pass, the laser beam removes a fixed amount of the seal ring material therefrom by material ablation wherein the ring material is vaporized. For areas that do not overlap, equal amounts of material are removed. However, in each area where the laser beam passes overlap, material is removed during each pass such that the overlap area has been cut deeper and therefore forms an overlap groove having a depth which is greater than the non-overlapped areas. Further, when a rectangular laser beam is used, the opposite ends of each groove formed by a pass of the laser are rectangular and as a result, adjacent ends are stepped across the seal face.
It therefore is an object of the invention to provide a seal ring having micro-topography features formed by multiple passes of a laser beam wherein the beam is shaped to prevent formation of overlap grooves having an excessive depth greater than the desired depth of the feature being formed. It is a further object of the invention to provide a method of forming micro-topography features in the seal ring which blends the laser cuts such that the peripheral edge or boundary of the micro-topography features is cut to a high degree of precision.
To achieve these objectives, the invention generally relates to a seal ring having precisely defined micro-topography depth features in the seal face and a method for forming these micro-topography features.
The micro-topography features are formed in the seal face by a shaped laser beam which removes material in multiple passes along the seal face. During formation of the micro-topography features, the laser beam first cuts through one or more passes along the same beam path to define a cut or groove. To form cuts having an increasing depth in the center thereof as is typically required for a wavy face seal, each successive pass on a single cut is shorter than the preceding pass so that more ablation passes are applied in the center of the cut than at the end of the cut. As a result, the cut has a variable depth whereby the depth increases or tapers away from at least one and possibly both of the opposite ends. The laser beam not only cuts multiple ablation passes along the same beam path, but also is shifted sidewardly to cut along adjacent beam paths. As a result, one or more additional adjacent or contiguous cuts or grooves ultimately define a micro-topography feature such as a valley of a wavy face, a radial groove or the like.
The method of the invention provides micro-topography depth features which are more precisely and accurately defined to improve performance of the seal ring. As the laser beam cuts the grooves one next to the other, each successive ablation pass along the groove overlaps the prior beam passes of the sidewardly adjacent groove to ensure complete coverage of the area of the seal surface on which the micro-topography feature is being formed and blend the edges of the sidewardly adjacent grooves together.
In this regard, the laser beam is shaped by a mask into a predefined geometric shape which illuminates the cutting surface whereby the opposite sides of the beam shape have non-linear side edges. These side edges define areas of the beam which will overlap with successive beam passes. For example, the mask in one embodiment includes a circular aperture through which the laser beam passes and is shaped so that the laser beam when striking the seal ring has a circular cross-section.
As the laser beam and seal ring move relative to each other during a continuous cutting process, the circular laser beam shape travels longitudinally and cuts a continuous ablation groove which is semi-circular when viewed from the side. The non-linear side edges of the beam travel longitudinally to define the opposite sides of the ablation groove. Due to the shape of the beam, the depth of the semi-circular groove is non-uniform along the lateral width thereof since a greater amount of ring material is removed at the center region and less material is removed from the opposite side edge regions of the laser beam. The shallower side regions define overlap areas that overlap an adjacent laser beam pass.
Unlike a rectangular shaped beam, the overlap areas of a beam having non-linear side edges may overlap to a significant degree, for example, up to 25% of a circular beam width yet the depth of the overlap area does not exceed the desired depth of the non-overlap areas. This thereby prevents formation of overlap grooves in the overlap area which exceed the maximum depth of the micro-topography feature being formed.
Besides a circular shaped laser beam, the beam may also be shaped to have other non-circular shapes. For example, the laser beam may have an elliptical shape or alternatively have linear edges in a center section with non-linear generally arcuate sections at the opposite ends of the center section. The arcuate side sections may be defined by continuous curves or by short linear sections which effectively define an arc. In these alternate beam shapes, the opposite side edges of the beam are non-linear to define an ablation cut in the seal face having a non-uniform depth.
The inventive seal ring and method for forming the seal ring provide distinct advantages in the formation of micro-topography depth features. For example, by providing a shaped laser beam and optimizing the overlap of the beam cuts, the inventive method eliminates or controls undesirable excessive-depth grooves in the overlapping areas extending along the sides of adjacent beam passes, and furthermore blends the ends of adjacent beam cuts to provide a boundary of the micro-topography features which are more arcuate or curved than the rectangular generally stepped edges resulting from a rectangular shaped laser beam.
The inventive method in the seal ring thereby not only provides a more repeatable and accurate manufacturing process, but also provide a significantly improved ability to construct a wide variety of micro-topography features.
Other objects and purposes of the invention, and variations thereof, will be apparent upon reading the following specification and inspecting the accompanying drawings.
Certain terminology will be used in the following description for convenience in reference only, and will not be limiting. For example, the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the system and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof, and words of similar import.